Three-stage process for hydrotreating feeds rich in polynuclear aromatics

ABSTRACT

DISCLOSED IS A THREE-STAGE PROCESS FOR CONVERTING INTO GASOLINE AND DISTILLATE FUELS A HYDROCARBON FEED RICH IN POLYNUCLEAR AROMATICS. THE FIRST STAGE EMPLOYS A CATALYST COMPRISING AN ALKALI METAL COMPONENT OR AN ALKALINE EARTH METAL COMPONENT OR BOTH, SUPPORTED ON ACTIVATED CARBON. THE SECOND AND THIRD STAGES EMPLOY A CATALYST COMPRISING METALLIC COMPONENTS FROM GROUP VI AND GROUP VIII OF THE PERIODIC TABLE, SUPPORTED ON A REFRACTORY, INORGANIC CRACKING MATRIX.

Aprii 10, 1973 A. w. FRAZIER ETAL 3,726,187 THREESTAGE PROCESS FOR HYDROTREATING FEEDS RICH IN POLYNUCLEAR AROMATICS Filed Oct. 14, 1971 2 Sheets-Sheet 1 Heavy Oil Feed I /0 Makeup Hydrogen Light Hydrocarbons SEPARATION FACILITY 2 8 H S If Gasoline Distillate F RAG T/O/VA T/O/V 46 TOWER Recycle Oil M48 3 tea l/V VE/V TORS.

Alvin W. Frazier Maurice F. Oxenreifer A TTORNEY April 10, 1973' I w, FRAZER ETAL THREE5TAGE PROCESS FOR HYDROTREATING FEEDS RICH IN POLYNUCLEAR AROMATICS Filed Oct. 14, 1971 86 Res/d Feed sTAE STAGE 2 Sheets-Sheet 2 Fig. 2

GAS TREATING 74 GAS LIQUID SEPARATOR Liquid Product to Fractionation Tower Hydrocarbons United States Patent 3,726,787 THREE-STAGE PROCESS FGR HYDROTREATING FEEDS RICH IN POLYNUCLEAR AROMATICS Alvin W. Frazier, Chicago Heights, Ill., Maurice E. Oxenreiter, Dyer, Ind., and Arnold N. Wennerberg, Chicago, 11]., assignors to Standard Oil Company, Chicago, Ill.

Filed Oct. 14, 1971, Ser. No. 189,177 Int. Cl. Cg 13/02, 23/02 US. Cl. 208-59 7 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND Hydrocarbons including polynuclear aromatics, especially the resid fraction from crude oil, are frequently low value fuels available in large volumes. Present processes have been developed to coke such resids, crack them, deasphalt them and/or hydrocrack them and distill out a feed suitable for a fluidized cracking unit. Each of these processes leads to loss of the starting material to coke or a lower value fuel. It is the objective of our invention to convert essentially all of the hydrocarbon feed high in polynuclear aromatics to a valuable high octane gasoline or distillate fuel. Upon studying the accompanying description of our invention, it Will be evident that our process not only has the advantage that the low value resids can be converted to the more valuable gasoline and distillate fuels, but such conversion can also be done in an economic manner, employing a single hydrogen supply source, the same recycle compressor and an integral, single refinery unit, thus conserving on equipment and hydrogen.

THE INVENTION We have invented a three-stage hydrocracking process for converting into gasoline and distillate fuels hydrocarbons including polynuclear aromatics. The boiling range, at normal pressure ranges, of gasoline and distillate fuels is'between about 100 and about 650 F. as compared to a typical boiling range of about 650+ F. and higher for the hydrocarbon feed. Suitable feeds would preferably be resid hydrocarbons but bottoms from reformer units, shale oil, tar sands oil, or coal-derived liquids could also be used, either solely or combined with the resid hydrocarbons. Usually the feed contains polynuclear aromatics ranging from about 0.1 to about 30 wt. percent of the feed, and the feed may also include organic nitrogen and sulfur compounds. The organic nitrogen compounds typically comprise from about 0.0 to about 1.0 wt. percent of the feed and the organic sulfur compounds typically comprise from about 0.0 to about 6.0 wt. percent of the feed.

The key to the successful operation of our process is the first stage or reaction zone, where the polynuclear aromatics in the feed are hydrocracked. In this first reaction zone the feed contacts, at elevated temperatures and pressures and in the presence of hydrogen, a catalyst comprising activated carbon and an alkali metal component or an alkaline earth metal component or both. The amount of metal component is suflicient to promote cracking of 3,726,787 Patented Apr. 10, 1973 polynuclear aromatics. In some instances it may also be desirable to include metallic components from Groups VI and VIH of the Periodic Table such as, for example, nickel, tungsten, cobalt, molybdenum, iron, or their OX- ides or their sulfides.

Feeds including polynuclear aromatics having a number average molecular weight of about 400 or greater can most advantageously be treated according to our process. For example, resids include such polynuclear aromatics called asphaltenes and resins. The asphaltene concentration in, for example, a vacuum resid ranges between about 0.1 and about 30 wt. percent depending on its crude oil source, and the resin concentration ranges between about 25 and 70 Wt. percent. The resins and asphaltees are structurally similar materials; however, resins are generally of lower molecular weight, heptane soluble, and are adsorbed on the surface of silica gel when a heptane solution of resins and oils is passed over a column of silica gel. The asphaltenes have high molecular weights such as, for example, from about 1,000 to about 15,000 and are insoluble in hot heptane.

The catalyst used in the first reaction zone is somewhat selective. Present data indicate that the polynuclear aromatics, when treated according to this process, are converted to lower molecular weight aromatics including with some feeds substituent alkyl groups. It is desirable to maintain a high concentration of resins in the reaction mixture, since resins help maintain the asphaltenes in solution. Thus the asphaltenes will not precipitate and clog the reactor or form coke deposits on the catalyst. Present data indicate that this carbon catalyst promotes cracking of the polynuclear aromatics without the catalyst bed plugging for periods in excess of 720 hours. These data also indicate that our process can reduce the molecular weight of asphaltenes by a factor of about 10, and the molecular weight of resins by a factor of about 3. Consequently, resin concentration in the reaction mixture of our process is always relatively high, minimizing loss of asphaltene solubility. The tendency toward reactor plugging is thus greatly reduced. And, surprisingly, our catalyst cracks or otherwise modifies the metal-containing compounds in the resid, and the metals are deposited on our catalyst without any noticeable adverse effects during the time of our experiments. High molecular weight sulfur-containing compounds are also cracked in our process. Our catalyst, however, appears to have little effect on low molecular weight sulfur compounds commonly found in resids such as benzothiophene and dibenzthiophene. Hence, there can be virtually complete demetallization and partial desulfurization of the resid using our catalyst.

Specifically, the catalyst used in the first zone comprises activated carbon having a surface area in the range of from about 200 to about 2,500 square meters per gram of carbon. This catalyst can be in either powder or granular form. In the granular form the preferred surface area ranges fom about 800 to about 2,000 square meter per gram of carbon. This activated carbon is impregnated with the metal component which is preferably in the form of a hydroxide, sulfide or oxide. Preferred alkali metals are potassium, sodium, lithium, rubidium and cesium. Preferred alkaline earth metals are magnesium, calcium, strontium and barium. The concentration of metal typically varies from about 0.1 to about 50 wt. percent based on the weight of carbon.

In preparing the catalyst, a metal salt can be used as a starting ingredient. It is dissolved in water and then the aqueous solution can be mixed with the activated carbon. The water is then removed to deposit the salt on the carbon. Also, decomposable salt forms such as acetates or formates can be used as starting ingredients. These can be mixed with the carbon and heated so that the salts will decompose and the metals be deposited on the carbon surface. We have found the most preferred method of preparation to be dissolving a metal hydroxide in an alcoholic solution such as methanol, ethanol or propanol, mixing carbon with the solution and then removing the alcohol. The most preferred metal hydroxide is potassium hydroxide.

In the second and third stages or reaction zones the catalyst employed comprises metallic components from Groups VI and VIII of the Periodic Table supported on a refractory, inorganic cracking matrix. The metallic components may be in the metal, metal oxide, or metal sulfide form. The amount of metallic component ranges between about 1.0 and about 30 wt. percent based on the weight of the support material. Preferred support materials are silica-alumina, alumina, magnesia, zir- 4 dissolved in 85 ml. of warm water. The sample is dried at 250 F. and pelleted or extruded. The pellets or extrudates are calcined in air for 3 hours at 1000 F.

(3) Example of catalyst preparation for third reaction zone Eighty-two grams of silica-alumina powder were impregnated with 14.8 gram of cobaltous nitrate,

TABLE First zone Second zone Third zone Broad Broad Broad range Typical range Typical range Typical Temperature, F 750-850 810 600-800 700 650-800 Pressure, p s i n 500-4,000 2,000 600-3, 500 1,800 800-3,000 1,600 Feed rate, vols. of hydrocarbons/vol. of catalyst per hour. 0.1-3.0 .4 0. 5-5. 0 2.0 0.5-2.0 1. 0 Hydrogen feed rate, s.c.f. oi hydrogen/barrel of feed 2, DOG-20,000 5, 00 500-5, 000 1,500 2, 00020,000 10,000

conium and other such inorganic oxide metals. Zeolitic materials may also be used in the support, and it is especially desirable to include such materials in the catalyst used in the third reaction zone. Such catalysts are generally well known in the petroleum processing art.

The product withdrawn from the first zone is fed at elevated temperatures and pressures into the second zone where the catalyst is particularly adapted to promote the cracking of essentially all inorganic nitrogen and sulfur compounds remaining in the withdrawn product. The most preferred catalyst comprises tungsten and nickel components (sulfide form) supported on silica-alumina. The amount of nickel sulfide ranges between about 1.0 and about 10 wt. percent based on the weight of the support material, and the amount of tungsten sulfide ranges between about 1.0 and about 20 wt. percent based on the weight of the support material.

The product from the second zone is withdrawn and is fed into the third reaction zone, at elevated temperatures and pressures, where it contacts the catalyst that promotes the cracking of this withdrawn product into a low boiling fuel. The most preferred catalyst for this purpose comprises cobalt and molybdenum components (oxide form) on silica-alumina. The amount of cobalt ranges between about 1.0 and about 10 wt. percent based on the weight of the support material, and the amount of molybdenum ranges between about 1.0 and about 0 wt. percent based on the weight of the support.

(1) Example of catalyst preparation for first reaction zone To prepare a catalyst which includes Wt. percent potassium hydroxide based on the weight of carbon, first prepare, at 70 F. 100 grams of a methanol solution including 20 grams of potassium hydroxide dissolved in 80 grams of methanol. Seventy grams of activated carbon is then mixed with this solution and the methanol is evaporated. A preferred carbon is manufactured by Pittsburgh Carbon and Chemical Company, designated as SGL active granular carbon, mesh size 20-30, and having a surface area of about 800 square meters.

(2) Example of catalyst preparation for second reaction zone Eighty-two grams of silica-alumina powder were impregnated with 14.8 grams nickelous nitrate,

NiNO3'6H2O and 20.6 grams ammonium metatungstate,

( U s a la to DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 schematically depicts one embodiment of the process of our invention. In this embodiment three reactors 10, 12 and 14 are connected in series. Hydrogen from source 16 is fed through compressor 18 and line 20 to the top of reactor 10 where it is mixed with feed from source 22. The feed may be any hydrocarbon including polynuclear aromatics and preferably is a resid hydrocarbon, bottoms from reformer units, shale oil, or mixtures thereof.

Reactor 10 includes the carbon supported catalyst, as described, which is particularly adapted to crack the polynuclear components of the feed. The catalyst is preferably in a fixed bed and the feed and hydrogen flow downwardly through the bed. The feed also normally includes some organic nitrogen and sulfur compounds and the catalyst does promote some cracking of these materials. Thus hydrogen sulfide, ammonia and light hydrocarbons (C or less) are formed in reactor 10 and withdrawn from the bottom of this reactor via line 24. These gases and hydrogen fiow via line 24 into compressor 26 which feeds them to separation facilities 28 where the light hydrocarbons, hydrogen sulfide and ammonia are withdrawn from the system. The hydrogen is recycled via lines 30 and 20 to the top of reactor 10. A liquid hydrocarbon is also withdrawn from reactor 10 via valved line 32. This material is the first intermediate product which is essentially free of polynuclear aromatics but contains some organic nitrogen and sulfur compounds. In this first intermediate product the percent nitrogen typically is about 0.2 wt. percent or less, and the sulfur is typically 1.5 wt. percent or less.

The liquid product from reactor 10 flows into the top of reactor 12. Hydrogen from line 30a also flows into the top of reactor 12 and is mixed with the liquid product from reactor 10. Reactor 12 contains the catalyst, as described, which is particularly adapted to crack the organic nitrogen and sulfur compounds in the liquid product from reactor 10. This catalyst is preferably in a fixed bed and the products flow downwardly into this bed, with the organic nitrogen and sulfur compounds and some hydrocarbons being cracked to form ammonia, hydrogen sulfide and hydrocarbon gases. These gaseous materials are withdrawn via line 34 which feeds them into line 24. where they are forwarded via compressor 26 to separation facilities 28. A second intermediate product, essentially free of nitrogen and sulfur compounds, is withdrawn from reactor 12 via valved line 36.

This second intermediate product and some hydrogen from line 30b flow into the top of reactor 14. Reactor 14 holds a fixed bed of catalyst, as described, which is particularly adapted to promote cracking of the second intermediate product into low boiling fuel. The second intermediate product and hydrogen flow downwardly through reactor 14. Hydrocracking occurs within the reactor to consume some of the hydrogen. Unused hydrogen is withdrawn via line 38 and forwarded to compressor 26 for recycling. An efiiuent leaves reactor 14 via valved line 40 which is rich in low boiling fuel components. This eflluent is forwarded to fractionation tower 42 where it is distilled, with gasoline being withdrawn from line 44, distillate fuel being withdrawn from line 46, and heavier materials being withdrawn via line 48 and recycled through pump 50 and line 52 to valved line 36 for reprocessing.

FIG. 2 schematically depicts a second embodiment of the process of our invention wherein a single reactor 60 is utilized. This reactor includes three contiguous, fixed beds of catalyst 62, 64 and 66. Beds 62 and 66 are separated from bed 64 by screens 68. Bed 62 includes the carbon catalyst adapted to hydrocrack polynuclear aromatics, bed 64 includes the catalyst which promotes desulfurization and denitrification of hydrocarbons, and bed 66 includes the catalyst which promotes hydrocrackin-g of hydrocarbons to low molecular weight components suitable for gasoline and distillate fuels. Hydrogen from source 70 is mixed with resid feed from source 72. This hydrogen-resid mix flows downwardly through the three fixed beds of catalyst. In bed 62 the polynuclear components are hydrocracked, in bed 64 the organic nitrogen and sulfur compounds are hydrocracked to form ammonia and hydrogen sulfide, and in bed 66 the hydrocarbons are converted to hydrocarbon materials suitable for blending in gasoline or distillate fuels. Effiuent from the bottom of reactor 60 flows into a gas liquid separator 74. Liquid product is withdrawn via line 76 and forwarded to a fractionation tower, and gases are withdrawn via line 78 and pumped by pump 80 into gas treating facilities 82 where hydrogen sulfide, ammonia and hydrocarbon gases are separated from hydrogen. Hydrogen is recycled via line 84 through compressor 86 to the top of reactor 60 where it is mixed with make-up hydrogen from source 70 and resid feed.

We claim:

1. A process for converting into low boiling material hydrocarbons including organic nitrogen and sulfur compounds and polynuclear aromatics, comprising the steps of:

(a) contacting, at elevated temperatures and pressures,

said hydrocarbons in a first reaction zone with hydrogen and a catalyst comprising activated carbon and an alkali metal component or an alkaline earth metal component or both, said metal component being present in an amount sufficient to promote cracking of said polynuclear aromatics, whereby a first intermediate product is formed,

(b) contacting, at elevated temperatures and pressures, said first intermediate product in a second reaction zone with hydrogen and acatalyst that promotes cracking of essentially all organic nitrogen and sulfur compounds in said first product, whereby a second intermediate product is formed, and

(c) contacting, at elevated temperatures and pressures, said second intermediate product in a third reaction zone with hydrogen and a catalyst that promotes cracking of said second intermediate product into said low boiling materials.

2. A process for converting into low boiling material hydrocarbons including organic nitrogen and sulfur compounds ranging from about 0.0 to about 6.0 wt. percent of the feed, and polynuclear aromatics ranging from about 0.1 to about 30 wt. percent of the feed, comprising the steps of:

(a) contacting said hydrocarbons in a first reaction zone with hydrogen and a catalyst comprising an activated carbon having a surface area in the range of from about 200 to about 2,500 square meters per volume of catalyst and from about 0.1 to about 50 wt. percent of an alkali metal component or an alkaline earth metal component or both, based on the weight of the carbon, conditions within said first reaction zone being: a temperature of from about 750 to about 850 F., a pressure of from about 500 to about 4000 p.s.i.g., and a feed rate of from about 0.1 to about 3.0 volumes of hydrocarbons per volume of catalyst per hour;

(b) withdrawing product from said first zone and contacting said withdrawn product in a second reaction zone with hydrogen and a catalyst comprising a refractory, inorganic cracking matrix supporting from about 1.0 to about 30 wt. percent, based on the weight of the matrix, of a metallic component from Group VI or Group VIII of the Periodic Table, said conditions within the second zone being: a temperature of about 600 to about 800 F., a pressure of from about 600 to about 3500 p.s.i.g., and a feed rate of from about 0.5 to about 5.0 volumes of hydrocarbons per volume of catalyst per hour;

(0) withdrawing product from said second zone and contacting said withdrawn product in a third reaction zone with hydrogen and a catalyst comprising a refractory, inorganic cracking matrix supporting from about 1.0 to about 30 wt. percent, based on the weight of the matrix, of a metallic component from Group VI or Group VIII of the Periodic Table, said conditions within said third reaction zone being: a temperature of from about 650 to about 800 F., a pressure of from about 800 to about 3000 p.s.i.g., and a feed rate of from about 0.5 to about 2.0 volumes of hydrocarbons per volume of catalyst per hour; and

(d) Withdrawing from said third reaction zone a product rich in hydrocarbons boiling in the range of from "about to about 650 F. at normal pressures.

3. The process of claim 1 wherein the catalyst in said second and third reaction zones comprises a Group VI or Group VIII metal component supported on a refractory, inorganic cracking matrix.

4. The process of claim 1 wherein the reaction condi tions are:

first zone:

Temperature of about 750 to about 850 F.

Pressure from about 500 to about 4000 p.s.i.g.

Feed rate of about 0.1 to about 3.0 volumes of hydrocarbons per volume of catalyst per hour Hydrogen feed rate of about 2000 to about 20,000 standard cubic feet of hydrogen per barrel of feed.

second zone:

Temperature of about 600 to about 800 F.

Pressure from about 600 to about 3500 p.s.i.g.

Feed rate of about 0.5 to about 5.0 volumes of hydrocarbons per volume of catalyst per hour Hydrogen feed rate of about 500 to about 5000 standard cubic feet of hydrogen per barrel of feed.

third zone:

Temperature of about 650 to about 800 F.

Pressure from about 800 to about 3000 p.s.i.g.

Feed rate of about 0.5 to about 2.0 volumes of hydrocarbons per volume of catalyst per hour Hydrogen feed rate of about 2000 to about 20,000 standard cubic feet of hydrogen per barrel of feed.

5. The process of claim 4 wherein the catalyst in said first zone comprises an activated carbon having a surface area in the range of about 200 to about 2,500 square meters per gram of carbon and from about 0.01 to about 50 wt. percent of an alkali metal component or an alkaline earth metal component or both, based on the weight of the carbon.

7 8 6. The process of claim 5 wherein the catalyst in the 2,801,208 7/1957 Horne et a1 208-61 second zone comprises nickel and tungsten components 2,877,176 3/1959 Wolff et a1. 208-208 on silica-alumina, and the catalyst in the third zone com- 2,971,901 2/1961 Halik et a1. 208-59 prises cobalt and molybdenum components on silica- 2,991,242 7/1961 Branton et a1. 208-134 alumina. 5 3,546,103 12/ 1970 Hamner et a1. 208-211 7. The process of claim 5 wherein the alkali metal cOm- 3,600,299 8/ 1971 Koller 208-89 ponent or alkaline earth metal component in the catalyst in the first reaction zone is in the form of a hydroxide, DELBERT GANTZ, Primary el' sulfide Mide- G. E. SCHMITKONS, Assistant Examiner References Cited 10 UNITED STATES PATENTS US. Cl. X.R.

1,922,542 8/1933 Krauch et al. 208-10 208-58, 216, 254

1,938,542 12/1933 Pier et al. 208-10 

